SU1662819A1 - A method of surface protection in jet-abrasive ejectors - Google Patents

Abstract

The invention relates to mechanical engineering and can be used in various units to protect their surfaces from the effects of two-phase or other jets. The purpose of the invention is to increase the efficiency of surface protection. The main stream supplied to the channel of the ejection apparatus is an abrasive with energy carrier. The working nozzle 6 consists of telescopically connected annular elements that form supersonic parietal nozzles 8 among themselves. Supersonic underexpanded wall streams with profiles 17 start from output sections 18 of supersonic nozzles and have characteristic sections 19 of locking and isobaric sections 20. The distance between supersonic circuits in the axial direction, α = α _with ... α _zap , where α _with , α _zap are the distances from the exit section of the nozzle to the isobaric section and to the section of locking, respectively. Maintaining these distances increases the pressure of the near-wall streams from the condition that the abrasive particles stop contacting the surfaces of the apparatus. 2 ill., 1 tab.

Description

The invention relates to the treatment of surfaces of parts with a jet and can be used in mechanical engineering in various units to protect their surfaces from the effects of two-phase or other jets, in particular in plasma torches to prevent the sprayed powder from directing to the inner surfaces of the nozzle when the powder is introduced to the anode spot.

The aim of the invention is to increase the effectiveness of surface protection.

Figure 1 shows the jet-abrasive apparatus with which the proposed method is carried out, a longitudinal section; figure 2 - scheme of near-wall protective flows.

The jet-abrasive ejection apparatus contains channels 1-3 for supplying an abrasive with energy carrier, additional and protective energy carriers, mixing chambers 4.5 additional and protective energy carriers, a working nozzle 6 and nozzles 7 and 8 of additional and protective energy carriers. The working nozzle 6 consists of telescopically connected annular elements 9, the inner surfaces of which form between themselves supersonic parietal annular nozzles 8. The power supply line of the protective energy carrier is equipped with a pressure reducer 10, Each annular element 9 can be equipped with a vibration sensor 11 and an external drive 12 of reciprocating motion with

ABOUT

about

K) 00

Yu

latch position. A pressure reducer 10 and a vibration sensor 11 with an amplifier 13 and an amplitude analyzer 14 are connected to an external drive 12 via a controller 15 and a relay 16, respectively. The supersonic near-wall flows with profiles 17 come from the output sections 18 of the supersonic nozzles 8 and have characteristic locking sections 19 and isobaric sections 20. The ring elements 9 contain seals 21.

In the drawings, the following notation is accepted: Pax - energy carrier pressure at the entrance to the supersonic nozzle; K is a section in a supersonic near-wall jet, in which the pressure ratio P3X is the static pressure in this section is critical; Pk is the static pressure in section K of a supersonic parietal jet; PH - pressure in the working nozzle 6; U is the length of the supersonic jet to the section K; C is the length of the supersonic jet to the isobaric section; yap is the length of the supersonic jet to the section of the shut-off.

Jet-abrasive ejection apparatus operates as follows.

Additional and protective energy is fed to the working nozzle 6 through channels 2 and 3, respectively. In this case, in accordance with the pressure of the protective energy carrier, by means of the regulator 15, the external drive 12 determines the distance between the supersonic nozzles of the protective energy carrier 8, equal to L Lc -L3an. Then, an abrasive with energy carrier is supplied to the working nozzle 6 via channel 1, and with the aid of the gearbox 10 the pressure of the protective energy carrier is gradually increased. Depending on this pressure, the distance between the supersonic nozzles 8, L c -Cap, is maintained by means of the displacement controller 15 by the external drive 12. The pulses from the blows of abrasive particles against the walls of the working nozzle 6 are recorded by the vibration sensor 11 and arrive through the amplifier 13 and the amplitude analyzer (allowing to distinguish among vibrations caused by gas-dynamic noise, impulses from the blows of the abrasive particles) to the relay controller 16. The pressure of the protective energy carrier continues to increase until the abrasive particles come into contact with the inner surface of the working nozzle b, after which the relay controller 16 turns off the external actuator 12 and sends a control signal to stop Pressure increase in the reducer 10. The tightness between the outer cylindrical surfaces of the annular elements is provided by seals 21. If necessary, maintaining a constant length of the working nozzle, the final annular element is fixed relative to the body of the apparatus (not shown, but). In this case, with an increase in the supply pressure of the protective energy carrier, some ring elements enter into others, for example, in the outlet part of the working nozzle; and although the distance between the two last ring elements will not be maintained with L Lc-L3an, protection of the inner surface of the working nozzle between them will be ensured by the previous supersonic nozzle in front of them.

5 During operation of the jet-abrasive ejection apparatus, the main stream, which is emitted by an additional energy source emitting from the nozzle 7, is an abrasive stream coming

0 from channel 1, is pressed by near-wall underexpanded supersonic flows emanating from nozzles 8. The release occurs due to the fact that at the length L3an the boundary of the supersonic jet has

5 is highly resistant to disturbances from outside, including in the form of individual particles (for example, abrasive). This is due to the elastic properties of the jet boundary, since in the case of a supersonic

As the flow rate decreases, the flow cross section reduces its flow and increases its pressure. The protective properties of an underexpanded supersonic jet appear as follows. When elasticity

5 the supersonic jet is not enough and the particle still breaks its boundary, then at the moment the particle penetrates the jet by an amount approximately equal to its radius, the supersonic flow ahead of the particle locally decelerates, which causes an increase in pressure. Due to the significant difference in pressure acting on the particle in this case from the side of the main and near-wall supersonic flows, parts of the center are pushed out by the near-wall flow,

without having to touch the wall of the working nozzle.

On the other hand, to the isobaric

sections (sections in which the static

the pressure in the wall jet is equal to the pressure in the main flow), i.e. in the interval of lengths 0 L C, there is a section K, in

Where pressure ratio is

critical since this attitude on

five

the length L 0-Lc varies from subsonic to one to the disposable supersonic ratio / PH. Therefore, if we arrange the output sections of the subsequent nozzles relative to the previous ones on the length L from 0 to, then the ratio Pa / Pk will be subcritical, and the flow will be subsonic or even locked (discontinued). The subsonic flow of each subsequent wall jet inhibits the previous supersonic jet and leads to their active outweighing, which reduces the stability of the supersonic jet, enhances the blurring of its boundaries and weakens the protective properties. In connection with this, supersonic nozzles are located relative to each other over the length Lc L L3an.

The proposed method was carried out on a jet-abrasive ejection apparatus (Fig. 1). The inner surfaces of the annular elements were made of mild steel, their radii were (R Tr) 20.21 and 22 mm, respectively, for the initial, middle, and final portions. The nozzle capacity was about 0.9 t / t.

The consumption of additional energy was 0.125 kg / s at a supplied pressure of 4 kg / cm. Air was used as an additional and protective energy carrier. Supersonic near-wall flows were created by annular nozzles at an outflow rate corresponding to the Mach number Ma-1, with output sections of 1.22; 1.29 and 1.35 cm (the width of the annular sections in all nozzles was 1 mm) and with zero angles between the tangents to the nozzle generators and their axes. The lengths of the ring elements are chosen so that the distance between the supersonic wall nozzles can be adjusted according to the applied pressure of the protective energy carrier according to the dependence obtained from a one-dimensional calculation for a variety of points as a result of solving the continuity equation and the amount of motion and the subsequent quadratic approximation of the results :

L- (1.32-4.48) -10 4 -P02 + (2.766-5.03) 102 P0- {2.2-37.69)

L L / RTp;

where P0 is the ratio of the applied davGN

laziness of the protective energy carrier to pressure in the working nozzle 6.

The supply pressure of the protective energy carrier varied from 25 to 5 kg / cm (at first, modes with high pressures were studied), which corresponds to a distance of 5, a and 5 mm for the distance from the last supersonic nozzle to the outlet section of the working nozzle, respectively. For initial ring elements this corresponds to, 3 and 1.6 (subcritical ratio), a and 5 mm. Steel grit with a diameter of 0.8 and 2 mm was used as abrasive particles. The total operating time on each mode corresponding to a certain value of P0 and the particle diameter was 10 minutes, then the state of the inner surface of the working nozzle was visually monitored.

Traces of damage to the inner surface of the working nozzle of both particle diameters of the fraction appear at Po 5.

The table shows the results of observations.

The distance between supersonic nozzles in the direction of the main flow can be selected using the calculated dependence or experimentally.

Thus, the use of the proposed method of protecting surfaces in the jet-abrasive ejection apparatus and device for its implementation makes it possible to completely quench the velocity of the particles in the normal direction to the walls of the working nozzle, and therefore avoid contact of the particles with the internal surfaces of the apparatus and wear them. In addition, due to the acceleration of the main stream by supersonic near-wall streams, the energy characteristics of the jet are increased, and the use of vibration sensors and an external reciprocating drive protects the internal surfaces of the ejection apparatus when its modes of operation and abrasive particles change and achieve this by moving the annular elements of the working nozzle each other.

Claims (1)

Formula of Invention The method of protecting surfaces in a jet-abrasive ejection apparatus, which consists in creating multiple wall streams, characterized in that, in order to increase the efficiency of surface protection, wall streams are created using supersonic nozzles with underexpanded supersonic, spaced apart from each other in the axial direction and distance L Ц -L3an and, maintaining these distances, increase the pressure of the near-wall streams because of the termination of the contact of abrasive particles with the surfaces of the apparatus, where C, L3an are the distances from you a nozzle section to section until the isobaric locking section respectively. No. / J-jr . Basic PH--. E., flow -Jr . -. ft I J FIG. 2